Release Of Extracellular Products Research Articles

Temperature sensitivity of dark CO2 fixation in temperate forest soils

Abstract. Globally, soil temperature to 1 m depth is predicted to be up to 4 ∘C warmer by the end of this century, with pronounced effects expected in temperate forest regions. Increased soil temperatures will potentially increase the release of carbon dioxide (CO2) from temperate forest soils, resulting in important positive feedback on climate change. Dark CO2 fixation by microbes can recycle some of the released soil CO2, and CO2 fixation rates are reported to increase under higher temperatures. However, research on the influence of temperature on dark CO2 fixation rates, particularly in comparison to the temperature sensitivity of respiration in soils of temperate forest regions, is missing. To determine the temperature sensitivity (Q10) of dark CO2 fixation and respiration rates, we investigated soil profiles to 1 m depth from beech (deciduous) and spruce (coniferous) forest plots of the Hummelshain forest, Germany. We used 13C-CO2 labelling and incubations of soils at 4 and 14 ∘C to determine CO2 fixation and net soil respiration rates and derived the Q10 values for both processes with depth. The average Q10 for dark CO2 fixation rates normalized to soil dry weight was 2.07 for beech and spruce profiles, and this was lower than the measured average Q10 of net soil respiration rates with ∼2.98. Assuming these Q10 values, we extrapolated that net soil respiration might increase 1.16 times more than CO2 fixation under a projected 4 ∘C warming. In the beech soil, a proportionally larger fraction of the label CO2 was fixed into soil organic carbon than into microbial biomass compared to the spruce soil. This suggests a primarily higher rate of microbial residue formation (i.e. turnover as necromass or release of extracellular products). Despite a similar abundance of the total bacterial community in the beech and spruce soils, the beech soil also had a lower abundance of autotrophs, implying a higher proportion of heterotrophs when compared to the spruce soil; hence this might partly explain the higher rate of microbial residue formation in the beech soil. Furthermore, higher temperatures in general lead to higher microbial residues formed in both soils. Our findings suggest that in temperate forest soils, CO2 fixation might be less responsive to future warming than net soil respiration and could likely recycle less CO2 respired from temperate forest soils in the future than it does now.

Chitosan based nanoparticles as protein carriers for efficient oral antigen delivery

This study aimed to investigate the efficacy of nanoparticles based on chitosan as a vehicle for oral antigen delivery in fish vaccination. Carboxymethyl chitosan/chitosan nanoparticles (CMCS/CS-NPs) loaded extracellular products (ECPs) of Vibrio anguillarum were successfully developed by ionic gelation method. The prepared ECPs-loaded CMCS/CS-NPs were characterized for various parameters including morphology, particle size (312±7.18nm), zeta potential (+17.4±0.38mV), loading efficiency (57.8±2.54%) and stability under the simulated gastrointestinal (GI) tract conditions in turbot. The in vitro profile showed that the cumulative release of ECPs from nanoparticles was higher in pH 7.4 (58%) than in pH 2.0 (37%) and pH 4.5 (29%) after 48h. Fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) was used as model protein antigen and encapsulated in CMCS/CS-NPs for investigating the biodistribution of antigen after oral delivery to turbot in 24h. Oral immunization of ECPs-loaded CMCS/CS-NPs group in turbot showed elevated specific antibody and higher concentrations of lysozyme activity and complement activity in fish serum than ECPs solution. CMCS/CS-NPs loaded with ECPs could enhance both adaptive and innate immune responses than the group treated with ECPs solution and suggested to be a potential antigen delivery system.

Estimation of the phytoplankton productivity in three Estonian lakes

INTRODUCTION Light provides the energy necessary for the transformation of inorganic matter into organic matter by the planktonic algae and all other photoautotrophic plants. Primary production is the direct product of photosynthesis, and primary productivity is the sum of all photosynthetic rates in an ecosystem (Fee, 1998). Information on the primary production enables to improve the understanding of food web relationships in aquatic ecosystems. Because of changing light conditions, primary production has a pronounced diel pattern. In order to acquire integrated results over longer time periods (days, months, years), many consecutive measurements of instantaneous photosynthesis rate should be carried out and integrated. In some studies (Joniak et al., 2003; Yoshida et al., 2003; Forget et al., 2007) the values of daily primary production integrated over the photic zone were estimated from in situ incubations. However, such approach gives reliable results only in clear waters, while in highly productive waters incubation cannot be performed during a long period (e.g. from morning to evening) as part of the [sup.14]C-label gets lost from the cells during long-term incubation due to respiration of photosynthetic products (Lancelot & Mathot, 1986) and release of extracellular products (holler Jensen, 1985). Bio-optical model calculations could provide an alternative to the time-consuming 14C method. Several studies estimate primary production from light intensity and abundance of phytoplankton pigments (cited in Arst et al., 2008a). In cases the processes of interest occur on a longer time-scale, it is common to ignore diurnal variations and use mean daily photosynthetically available irradiance (PAR) to force models of primary producers. Widely used methods include those where the dependence of photosynthesis on available light is expressed by an equation containing two parameters: the initial slope [[alpha].sup.[[beta] and the assimilation number [P.sup.B.sub.m] (Sathyendranath et al., 1989). In these models also data on the vertical profiles of the photosynthetically active radiation (PAR) (Einst [h.sup.-1] [m.sup.-2]) are needed. This is a rather complicated way and gives results on the basis of radiation integrated over the PAR region. For reliable description of primary production profiles, however, it is preferable to use a 'spectral approach', in which the model is based on spectral data of underwater quantum irradiance and absorption coefficients of phytoplankton (Sathyendranath et al., 1989; Smith et al., 1989; Schofield et al., 1990; Kyewalyanga et al., 1992; Kirk, 1994; Sosik, 1996; Arst et al., 2006, 2008a). Two versions (spectral and integral) of a semi-empirical model for calculation of the vertical profiles of primary production in lakes were elaborated by Arst et al. (2008a). The main difference between the models resides in the data on underwater irradiance (spectral or integral). Quantification of these models was performed using the data of in situ measurements of bio-optical parameters in three turbid Estonian lakes (Peipsi, Vortsjarv, and Harku) in 2003-2005. The objectives of the present study were (1) to demonstrate the variability of underwater quantum irradiance by calculating its spectral and diurnal variations at different depths of three lakes for all measurement days; (2) to compare in situ primary production measurement results obtained in 2007 2008 with corresponding model results; and (3) using model calculations to estimate the diurnal variability of the vertical profiles of primary production as well as the corresponding integrated (over water column) values. MATERIALS AND METHODS Study sites The measurements were carried out in three Estonian lakes: Peipsi, Vortsjarv, and Harku. Morphometric data and other parameters of the lakes are shown in Table 1. Lake Peipsi is a large shallow lake on the border of Estonia and Russia. …

The concentrations of hexadecane and inorganic nutrients modulate the production of extracellular membrane-bound vesicles, soluble protein, and bioemulsifier by Acinetobacter venetianus RAG-1 and Acinetobacter sp. strain HO1-N.

In the present study, we addressed the possibility that the production of both bioemulsifiers and membrane-bound vesicles may be a common feature of the growth of Acinetobacter spp. on alkanes, and we determined the extent to which the release of extracellular products by these organisms is regulated by the concentrations of the alkane substrate and inorganic nutrients. To accomplish this objective, we grew Acinetobacter venetianus RAG-1 and Acinetobacter sp. strain HO1-N with different concentrations of nutrients and assayed for extracellular products. The results indicated that the release of vesicles, soluble protein, and bioemulsifier was promoted in various degrees by higher concentrations of hexadecane and inorganic nutrients, while the specific activities of the bioemulsifiers were enhanced with lower nutrient concentrations. Based on our findings, we propose that under conditions of nutrient excess, these strains produce membrane-bound vesicles to function in "luxury uptake" of the alkane substrate for delivery and storage in the form of inclusions. Under the same conditions, soluble bioemulsifier and protein may perform auxiliary roles in cell desorption and (or) alkane uptake. With low concentrations of nutrients, the decreased production of vesicles, protein, and bioemulsifier and the increased activity of the emulsifier may represent a mechanism for reducing biosynthetic demands and conserving cellular material.

Release of extracellular products by phytoplankton with special emphasis on polysaccharides

Organic substances are released from phytoplankton cells during all phases of growth. Carbohydrates, especially polysaccharides, sometimes comprise 80–90% of the total extracellular release. Nutrient status profoundly affects the amount and composition of the exudate. Severe N- and P-limitation favours the release of carbohydrates that do not contain these elements. Increase in the medium NP ratio above the classical Redfield ratio of 16 increases the production of extracellular polysaccharides in laboratory cultures. The type and amount of polysaccharide excreted and the effects of nutrient limitation are often highly species-specific. The production by different species can vary by a factor of up to 50. The rate of release is best specified either as a relative rate of release (PER, percent of total carbon fixation) or as a specific rate. The absolute rate of release for the diatom Chaetoceros affinis was higher in the exponential than in the stationary phase, whereas the PER was 5 times higher in the stationary phase. The mechanisms for excretion in algae are still largely unknown. Both simple and facilitated diffusion may be involved for small molecules and more complex mechanisms for macromolecules. The chemical structures of the extracellular polysaccharides are often species-specific. For example, the marine diatoms C. affinis and C. curvisetus both produce a polysaccharide containing residues of rhamnose, fucose and galactose, but there are major differences in structure. Accumulation of gelatinous masses due to extracellular release by algae was observed in the Adriatic Sea during the summers of 1988–1991. Several species of diatoms and dinoflagellates are implicated, and the jelly is composed of polysaccharides and/or proteoglycans. Blooms of Phaeocystis in the southern part of the North Sea form gelatinous colonies with localised concentrations of up to 7 mg/1. These contain 55–90% of polysaccharidic mucilage.

Pelagic food web processes in an oligotrophic lake

Major pelagic carbon pathways, including primary production, release of extracellular products (EOC), bacterial production and zooplankton grazing were measured in oligotrophic Lake Almind (Denmark) and in enclosures (7 m3) subjected to artificial eutrophication. Simultaneous measurements at three days interval of carbon exchange rates and pools allowed the construction of carbon flow scenarios over a nineteen day experimental period. The flow of organic carbon was dominated by phytoplankton EOC release, which amounted from 44 to 58% of the net fixation of inorganic carbon. Gross bacterial production accounted for 33 to 75% of the primary production. The lower values of EOC release (44%) and bacterial production (33%) were found in the enclosures with added nutrients. The release of recently fixed photosynthetic products was the most important source of organic carbon to the bacterioplankton. Uptake of dissolved free amino acids was responsible for 52 to 62% of the gross bacterial production. Thus, amino acids constituted a significant proportion of the EOC. Zooplankton (< 50 µm) grazing on algae and bacteria accounted only for a minor proportion of the particulate production in May. Circumstantial evidence is presented that suggests the chrysophycean alga Dinobryon was the most important bacterial remover. The results clearly demonstrated EOC release and bacterial metabolism to be key processes in pelagic carbon cycling in this oligotrophic lake.

Characterization of Native Bacteria and Their Utilization of Algal Extracellular Products by a Mixed-Substrate Kinetic Model

Assimilation and mineralization og 14C labelled extracellular products (EOC) by native bacterial populations were followed in a diel study and from early spring through autumn in two eutrophic Danish lakes. Kinetic analyses according to a mixed-substrate kinetic model always revealed linear kinetics. The method was found useful in unveiling in situ specific algal-bacterial associations mediated through the release of EOC from the primary producers. Further, bacterial adaptation toward the phycosphere of Microcystis aeruginosa could be detected by following the shift in X-intercepts for the lines of net uptake and respiration during the development of a bloom of M. aeruginosa. By simultaneous measurements of particulate primary production, EOC release and transport of EOC to the bacteria by a differential filtration technique, it is shown that the method presented does not generally estimate changes in the kinetic parameters, but does reveal qualitative changes. It is concluded that the mixed-substrate method is a powerful approach for elucidating specific algal-bacterial associations in situ, even in highly complex eutrophic environments.

Studies of Uptake and Turnover of Glycollic Acid in the Menai Straits, North Wales

Measurements were made of the concentrations of glycollic acid, photosynthetic pigments and mineral nutrients (N, P and Si), of the cell numbers and species-composition of the phytoplankton, of the rates of photosynthesis and release of extracellular products, and of the salinity, tidal height, temperature and light intensity over two 24-h periods in the Menai Straits, North Wales (21-22 February and 17-18 April 1975). A less complete study was made on 5 August 1975. In addition the kinetic characteristics of glycollate uptake (turnover-time, affinity constant and maximum velocity of uptake) were determined in the laboratory for a sample of water collected from the Menai Straits on 5 August 1975; three sets of conditions were used: darkness, and light with and without a specific inhibitor for diatom growth (germanium dioxide). The level of glycollate varied diurnally in all three study periods; it was maximal (15-25 pg I-') during the morning on all three occasions. In the first study period glycollate level was significantly correlated with the rate of release of extracellular products, but not with any of the other properties measured. No significant correlations were found in the later studies. Diatoms appeared to play no part in the uptake of glycollate under the conditions used.

Selective stimulation of marine bacteria by algal extracellular products1

Two marine bacterial isolates differ considerably in their uptake rates of extracellular products produced by the alga Skeletonema costatum: 0.4 × 10−8 µg C cell−1 hr−1 for spirillum 7697; 16 × 10−8 µg C cell−1 hr−1 for pseudomonad HNY. These disparate uptake rates are used to interpret the growth patterns of the bacteria in the presence of the alga on a seawater inorganic enrichment medium. Pseudomonad HNY grows well with the alga in both batch and continuous culture, in the latter attaining a steady state population two orders of magnitude greater than achieved in the absence of the alga. Spirillum 7697, however, grows poorly in the presence of growing algal cells and appears to be inhibited to some extent under such conditions. Such observations suggest that dominant bacterial populations associated with algal blooms are a result of both stimulation and inhibition mediated by the release of extracellular products.